1. Field of the Invention
The inventions disclosed and taught herein relate generally to uninterruptible power supplies; and, more specifically, relate to paralleled, multi-moduled uninterruptible power supplies.
2. Description of the Related Art
Uninterruptible power supplies (UPSs) are employed in an ever-increasing variety of situations where a constant source of power is desired. A typical UPS includes a rectifier section that converts alternating current energy (“AC”) into direct current energy (“DC”). The rectifier section is configured to be coupled to an AC power source, such as a public utility. An inverter section is coupled to the rectifier section and converts DC energy into AC energy, and thereby provides AC energy at an output of the UPS. The UPS may further include, or be coupled to, a backup source of power, such as a battery bank that can feed either AC or DC energy to the UPS when the primary power source is off-line or when the rectifier/inverter sections are disabled.
UPSs also typically include a bypass circuit to bypass the rectifier/inverter sections and couple the primary AC power source directly to the output bus of the UPS. The bypass circuit, which may be a static switch, can be used, for example, to provide an economy mode of operation and/or to provide power to the load when either or both of the rectifier or inverter sections are damaged or inoperative.
It is known that UPS bypass circuits may create problems in applications using multiple UPSs in parallel to feed a common load, such as a load bus. For example, if the UPS bypass circuit is closed, energy may be backfed from the common load bus through the closed bypass circuit onto the primary power source or into the UPS' power module.
U.S. Patent Application Publication No. 2005/0288826 purports to disclose a method and apparatus for UPS bypass monitoring and control in which the “status of a bypass source of parallel-connected UPSs is determined from a load share when a loading of the parallel-connected UPSs meets a predetermined criterion. Status of a bypass source of the parallel-connected UPSs is determined from a bypass source voltage when the loading of the parallel-connected UPSs fails to meet the predetermined criterion. The loading may include an aggregate loading, and failure of a bypass source of a UPS may be identified responsive to detecting that a load share of the UPS is less than a predetermined proportion of the aggregate loading. Alternatively, failure of the bypass source may be identified by detecting that a bypass voltage fails to meet a predetermined criterion. Bypass circuits of the UPSs may be controlled responsive to a load share and/or a bypass source voltage.”
U.S. Patent Application Publication No. 2006/0221523 purports to disclose “a method for controlling an uninterruptible power supply (UPS) for servicing a load. The UPS has a bypass feed path operable in parallel with an inverter feed path, the bypass feed path being engagable with the load via a first switch, and the inverter feed path and being engagable with the load via a second switch. The method includes: generating a paralleling detection signal indicative of the bypass feed path operating to service the load in parallel with the inverter feed path; and, in response to the presence of the paralleling detection signal, modifying a control signal to an inverter such as to drive toward equalization the bypass current and the inverter current. As a result, and in response to the two paths operating to service the load in parallel, the method tends to cancel circulation current generated between the bypass feed path and the inverter feed path.
U.S. Patent Application Publication No. 2003/0184160 purports to disclose a parallel operation method for an uninterruptible power supply apparatus, “the method being also capable of conducting a parallel non-redundancy operation of uninterruptible power supply apparatuses and having a bypass circuit incorporated therein without using an additional common circuit. In the parallel operation method for uninterruptible power supply apparatus of operating in parallel a plurality of uninterruptible power supply apparatuses, each having two operational modes including a bypass feeding mode and an inverter feeding mode, an off instruction for the AC switch is produced in the respective uninterruptible power supply apparatuses which are operated in parallel. The off instruction is produced based on a detection result showing coincidence of a pattern of (pattern coincidence detecting circuits 1002, 2002) the bypass feeding signal which is active during the bypass feeding state and a pattern of a ready signal which becomes active when the inverter feeding is ready for conducting.”
The inventions disclosed and taught herein are directed to an improved method and apparatus for bypassing the rectifier/inverter sections of a UPS and/or the entire UPS system for purposes of performing maintenance on the UPS or discrete components of the UPS.